I would like to understand how LCAO may be used to construct the matrix to be solved for the molecular orbitals of two cases of molecules: 1) small molecules like H3 (or H3+, HF2-, H2O, CH4, etc. 2) groups or parts of molecules with delocalized pi-systems (including linear and cyclic hydrocarbons, crown ethers, carboxylate ions, etc.) Huckel theory instruction is readily available, but it is only supposed to apply to the case of conjugated pi-systems in hydrocarbons, i.e. a special case of part 2 of what I'm looking for. I wish to generalize this, to all very small molecules like the ones I listed, and also to delocalized pi-systems (within the framework of arbitrary larger molecules, which I presume need not be considered to affect that system much). Can anyone suggest where I should read or look (Internet sources are welcome too) to find this explanation laid out?